The NHANES data included information on height and weight, which are used to calculate a person’s body mass index. A BMI between 18.5 and 24.9 is considered normal. Someone with a BMI in the 25-to-29.9 range is considered overweight, and a BMI over 30 qualifies a person as obese. (You can calculate your BMI here.)

Women were much more likely to be obese than overweight, with 37% of women in the former category and 30% in the latter. Altogether, two out every three women in the U.S. were above a normal weight.

The proportion of men who were obese was almost as high as women – 35%. But that figure was lower than the 40% of men who were in the overweight zone. With both groups combined, three out of four men in the U.S. exceeded a normal weight.

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African Americans had the highest rates of obesity among both men (39%) and women (57%). The researchers found that 17% of black women and 7% of black men were extremely obese, meaning their body mass index was over 40.

Among the group labeled Mexican Americans, 38% of men and 43% of women were obese. For whites, 35% of men and 34% of women were obese. No data were reported for Asian Americans, who until recently have been undersampled in NHANES surveys.

Rates of overweight and obesity were comparable for younger (ages 25 to 54) and older (ages 55 and up) adults, according to the study.

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Being overweight or obese increases the risk of a variety of chronic health conditions, including Type 2 diabetes and cardiovascular disease. Extra weight can also make people more vulnerable to certain types of cancer. The more you weigh, the greater the health risk, according to the National Heart, Lung and Blood Institute.

“This is a wake-up call to implement policies and practices designed to combat overweight and obesity," study co-author Lin Yang, a research associate in Washington University's Prevention Research Center, said in a statement.

Among other things, such policies should encourage more physical activity and more healthful diets, Yang and her co-author, Dr. Graham Colditz, chief of the Division of Public Health Sciences, wrote in their study. They also called on primary care doctors to enhance their "efforts to prevent and treat obesity."

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